1. Field of the Invention
The present invention relates to a multi-turn hydraulic actuator used to open/close a passageway in the ground and sea industries including general industrial machines, oil refineries and chemical plants, and power generating plants, among others, and more particularly, a technical field in which an actuator comprising a hydraulic motor and a decelerator is used to control the opening/closing of a valve which controls the flow of a fluid flowing through a path of a conduit, or a lock which is installed at a passageway.
2. Description of the Related Art
In general, major types of valve driving systems include a butterfly valve, a gate valve and a plug valve, among others, according to valve forms. Each valve is automatically driven by a 90 degree-turn or multi-turn actuator suitably selected according to use-environments. Examples of actuators include electric actuators, pneumatic actuators and hydraulic actuators by forms. Two functions, i.e., a stabilized actuation performance and a semi-permanent life span, are recognized as the most important factors in the actuators.
To control a valve installed in an industrial conduit or a lock installed in a passageway, a shaft of the valve or lock needs to be rotated, to perform the opening/closing operation of the valve or lock. The valve performs its operation generally by using an actuator which is controlled remotely or in the spot.
A conventional multi-turn electric actuator generally used comprises: a control unit including a 3-phase inverter converting single phase power into 3-phase power; a 3-phase electric motor operated by the control unit; a multi-unit with a rotation shaft installed perpendicularly to be rotated in either direction by the driving of the 3-phase electric motor; and a passageway switching unit for opening/closing a passageway.
In the aforementioned multi-turn electric actuator, when electric power is applied to the control unit including the 3-phase inverter, the 3-phase electric motor is driven. The motive power generated in the 3-phase electric motor is transmitted to a worm gear through a gear inside the multi-unit, thereby ultimately driving a drive block of the passageway switching unit installed at an end of the rotation shaft. Consequently, the opening/closing of the valve is controlled by the torque.
Further, the conventional multi-turn electric actuator is structured to monitor the operation of the gear inside the multi-unit, to perceive the extent of opening the valve and the drive of the actuator. For this purpose, an analog detection method and a digital detection method are used. In the former, an additional shaft is directly connected to the gear, to detect the number of times of rotation of the shaft by using variable resistance. In the latter, the number of times of rotation of the shaft is detected by using a sensor.
In a manual method of manually operating the conventional multi-turn electric actuator, a manual switch lever is rotated by human power, to apply a change to a combination of the gear inside the multi-unit, thereby changing an automatic mode to a manual mode.
When using the manual switch lever to change the mode of the actuator to the manual mode, sufficient rotational radius and space are required to operate the manual switch lever. Moreover, since all of the 3-phase electric motor, control unit, multi-unit, passageway switching unit and terminal unit forming the multi-turn electric actuator are structured in a single unit, it is impossible to install the manual switch lever in such a small space.
Further, in the analog detection method to perceive the extent of opening the valve and the drive of the actuator, an assembling process is very complicated since many gears are combined. Moreover, since the gear combination needs to be mechanically changed in order to set or correct a display of the extent of opening, it is necessary to open a cover. Therefore, this is regarded as a very annoying factor.
Further, in the digital detection method, one central processing unit of high-capacity is included in the control unit, to be used for the control and communication of the actuator. In addition, the central processing unit is used for a sensor of detecting the extent of opening. Therefore, high standby electric power is consumed at the moment when the actuator is not driven.